In Edelson's disclosure, filed Mar. 7, 1995, titled "Electrostatic Heat Pump Device and Method", Ser. No. 08/401,038, now abandoned, incorporated herein by reference in its entirety, two porous electrodes were separated by a porous insulating material to form an electrostatic heat pump. In said device, evaporation and ionization of a working fluid in an electric field provided the heat pumping capacity. The use of electrons as the working fluid is disclosed in that application. In Edelson's subsequent disclosure, filed Jul. 5, 1995, titled "Method and Apparatus for Vacuum Diode Heat Pump", Ser. No. 08/498,199, an improved device and method for the use of electrons as the working fluid in a heat pumping device is disclosed. In this invention, a vacuum diode is constructed using a low work function cathode.
In Edelson's further subsequent disclosure, filed Dec. 15, 1995, titled "Method and Apparatus for Improved Vacuum Diode Heat Pump", Ser. No. 08/573,074, now U.S. Pat. No. 5,722,242, incorporated herein by reference in its entirety, the work function of the anode was specified as being lower than the work function of the cathode in order to optimize efficient operation.
In a yet further subsequent disclosure, filed Dec. 27, 1995, titled "Method and Apparatus for a Vacuum Diode Heat Pump With Thin Film Ablated Diamond Field Emission", Ser. No. 08/580,282, now abandoned incorporated herein by reference in its entirety, Cox and Edelson disclose an improvement to the Vacuum Diode Heat Pump, wherein a particular material and means of construction was disclosed to further improve upon previous methods and devices.
The Vacuum Diode at the heart of Edelson's Vacuum Diode Heat Pump may also be used as a thermionic generator: the differences between the two devices being in the operation of the diode, the types and quantities of external energy applied to it, and the provisions made for drawing off, in the instance of the thermionic converter, an electrical current, and in the instance of the Vacuum Diode Heat Pump, energy in the form of heat.
In Cox's disclosure, filed Mar. 6, 1996, titled "Method and Apparatus for a Vacuum Thermionic Converter with Thin Film Carbonaceous Field Emission", Ser. No. 08/610,599, incorporated herein by reference in its entirety, a Vacuum Diode is constructed in which the electrodes of the Vacuum Diode are coated with a thin film of diamond-like carbonaceous material. A Vacuum Thermionic Converter is optimized for the most efficient generation of electricity by utilizing a cathode and anode of very low work function. The relationship of the work functions of cathode and anode are shown to be optimized when the cathode work function is the minimum value required to maintain current density saturation at the desired temperature, while the anode's work function is as low as possible, and in any case lower than the cathode's work function. When this relationship is obtained, the efficiency of the original device is improved.
Many attempts have been made to find materials with low work function for use as cathodes for vacuum diodes and thermionic energy converters. Currently most research is in the field of cathodes for vacuum tubes. Research in thermionic converter technology is less intensive because of the difficulties of increasing thermionic emission of electrons from the flat surface, where field emission effect can not be applied. The practical importance of thermionic energy conversion is rapidly increasing due to increased needs for alternative energy sources. The most effective way of decreasing work function known today is the use of alkaline metal vapors, particularly cesium, and coating the emitter surface with oxide thin films. Use of Cs vapor is not without technical problems, and thin film coated cathodes generally show short lifetimes.